Patent application title: IMAGE DISPLAY APPARATUS

Abstract:

A driving circuit of a liquid crystal element is simplified, both an
improvement in light emission efficiency and a reduction in external
light reflection are attained, and a cost reduction is realized.

Claims:

1. An image display apparatus comprising:a display panel having a light
emitting element;a circular polarizing element having a retardation plate
and an optical element having a controllable liner polarizing function,
and being placed on a light emission side of the display panel such that
the display panel, the retardation plate and the optical element are
placed in this order, whereinthe controllable liner polarizing function
of the optical element in a light emission period of the light emitting
element is different from that in a non-light emission period of the
light emitting element.

2. The image display apparatus according to claim 1, whereinthe liner
polarizing function of the optical element in the light emission period
is intensified rather than that in the non-light emission period of the
light emitting element.

3. The image display apparatus according to claim 1, whereinthe light
emission period of the light emitting element is 1/30-1/5 of the
non-light emission period of the light emitting element.

4. The image display apparatus according to claim 1, whereinthe display
panel has a plurality of the light emitting elements, and further has a
control unit capable of setting, at a light emitting state or at a
non-light emitting state, all of the light emitting elements together and
whereinthe optical element comprises a single liquid crystal element
corresponding to a whole area in which all of the light emitting elements
are arranged.

5. The image display apparatus according to claim 1, whereinthe display
panel has a plurality of the light emitting elements arranged in a
matrix, and further has a control unit capable of setting, at a light
emitting state or at a non-light emitting state, an arbitrary number of
rows of the light emitting elements, and whereinthe optical element
comprises a plurality of liquid crystal elements of which number
corresponds to a total number of the light emitting elements in the
arbitrary number of rows.

8. An image display apparatus comprising:a display panel having a light
emitting element;a retardation plate and a liquid crystal element, being
placed on a light emission side of the display panel such that the
display panel, the retardation plate and the liquid crystal element are
placed in this order, whereina ratio of light transmitting through the
retardation plate and the liquid crystal element in a light emitting
period within one frame of driving the light emitting element is larger
than that in a non-light emitting period within one frame of driving the
light emitting element.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to an image display apparatus, and
relates, in particular, to a light emitting image display apparatus, such
as an organic EL display apparatus, having a reflection electrode.

[0003]2. Description of the Related Art

[0004]In recent years, an organic EL display using an organic
electroluminescence element (hereinafter, called "organic EL element") is
focusing attention. In a typical organic EL element, an organic layer
including a light emission layer with about several hundred nm thickness
is placed between a reflection electrode and a light transmitting
electrode. In such a configuration of element, the reflection electrode
reflects light (external light) incident from an outside into the element
regardless of light emission by the element. Therefore, under the
environment with intense external light, external light reflection
components are greater than light emission components of the element.
This leads to a decrease in the contrast of the organic EL display, and
the visibility is degraded.

[0005]To solve such a problem, a circular polarizing unit is arranged on
the organic EL element in a typical known technique. For example, a
technique related to a circular polarizing plate including a linear
polarization plate and a (1/4)λ wavelength plate (including a
plurality of birefringent plates) is disclosed (see Japanese Patent
Application Laid-Open No. H09-127885).

[0006]When the circular polarizing plate is arranged on the organic EL
element, the external light becomes clockwise or counterclockwise
circularly polarized light and enters the organic EL element. The
incident light is reflected after the reflection electrode of the organic
EL element circularly polarizes the incident light in the opposite
direction from the direction when the light has entered. When the light
enters again in the circular polarizing plate, the light becomes linearly
polarized light orthogonal to the axis of the linear polarization plate
after passing through the (1/4)λ wavelength plate and enters the
linear polarization plate. Therefore, the light is shielded by the linear
polarization plate. The effect significantly reduces the external light
reflection.

[0007]However, the configuration has a problem that the light emission of
the organic EL element is also reduced by the circular polarizing plate.
This is caused by the linear polarization plate used as a constituent
element of the circular polarizing plate, and the linear polarization
plate cuts about 50% of the light.

[0008]To solve such a problem, in place of the linear polarization plate
used as a constituent element of the circular polarizing plate, a
configuration using a liquid crystal element having a nematic liquid
crystal provided with a two-color pigment between substrates subjected to
a uniaxial orientation process is proposed (see Japanese Patent
Application Laid-Open No. 2000-113988). In the technique described in
Japanese Patent Application Laid-Open No. 2000-113988, the external light
reflection at a non-light emission part of the organic EL element is shut
off by the effects of a liquid crystal element without application of
voltage and of a (1/4)λ wavelength plate. On the other hand, at a
light emission part of the organic EL element, a voltage is applied to
the liquid crystal element to control absorption of light in a liquid
crystal layer, and the light emission of the organic EL element can be
extracted to the outside without loss.

[0009]However, in the technique disclosed in Japanese Patent Application
Laid-Open No. 2000-113988, the liquid crystal element needs to be driven
in accordance with the non-light emission part and the light emission
part of the organic EL element. Therefore, the liquid crystal element
needs to be arranged in accordance with the arrangement pattern of the
organic EL element. For example, if the organic EL element is arranged in
a matrix, the liquid crystal element also needs to be driven in a matrix
arrangement. In that case, not only the organic EL element, but also the
driving circuit of the liquid crystal element becomes complicated, and
the cost of the display may be high.

SUMMARY OF THE INVENTION

[0010]The present invention has been proposed in view of the foregoing
circumstances, and an object of the present invention is to provide an
image display apparatus capable of simplifying a driving circuit of a
liquid crystal element, attaining both an improvement in light emission
efficiency and a reduction in external light reflection, and realizing a
cost reduction.

[0011]An image display apparatus according to the present invention
comprises: a display panel having a light emitting element; a circular
polarizing element having a retardation plate and an optical element
having a controllable liner polarizing function, and being placed on a
light emission side of the display panel such that the display panel, the
retardation plate and the optical element are placed in this order,
wherein the controllable liner polarizing function of the optical element
in a light emission period of the light emitting element is different
from that in a non-light emission period of the light emitting element.

[0012]According to the image display apparatus of the present invention,
the optical element is driven in synchronous with the light emission
period and the non-light emission period within one frame of the light
emitting element. At this point, if the whole area of the image display
apparatus simultaneously performs light emission period/non-light
emission period in the drive method, the driving circuit of the liquid
crystal element can be simplified because the liquid crystal element can
also be driven all together throughout the whole area. Therefore, both an
improvement in light emission efficiency of the image display apparatus
and a reduction in external light reflection can be attained, and the
functions can be realized with low cost.

[0013]Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference to the
attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic overall diagram illustrating an example of an
image display apparatus according to embodiments of the present
invention.

[0015]FIG. 2 is a schematic diagram illustrating an example of an organic
EL panel according to the embodiments of the present invention.

[0016]FIG. 3 is a schematic enlarged cross-sectional view illustrating an
example of the organic EL element according to the embodiments of the
present invention.

[0017]FIG. 4 is a schematic diagram illustrating an example of a variable
circular polarizing unit used in the image display apparatus according to
the embodiments of the present invention.

[0018]FIGS. 5A, 5B and 5C are timing charts describing operations of the
organic EL panel and the variable circular polarizing unit according to
the embodiments of the present invention.

[0019]FIG. 6 is an example of configuration of a pixel circuit including
the organic EL element according to the embodiments of the present
invention.

[0020]FIG. 7 is a timing chart of signal lines of a first row, an n-th
row, and an N-th row according to a first embodiment of the present
invention.

[0021]FIG. 8 is a timing chart of signal lines of a first row, an n-th
row, and an N-th row according to a second embodiment of the present
invention.

[0022]FIGS. 9A and 9B are schematic diagrams illustrating an example of
the variable circular polarizing unit used in the image display apparatus
according to the embodiments of the present invention.

[0023]FIG. 10 is a timing chart of signal lines of a first row, a second
row, a (2n-1)-th row, and a (2n)-th row according to a third embodiment
of the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0024]Embodiments of an image display apparatus of the present invention
will be described with reference to the drawings.

[0025]<Schematic Configuration>

[0026]FIG. 1 is a schematic overall diagram illustrating an example of an
image display apparatus according to embodiments of the present
invention.

[0027]The image display apparatus according to the embodiments of the
present invention comprises a display panel having a light emitting
element having a reflection electrode. The image display apparatus also
comprises a circular polarizing unit including: a retardation plate; and
an optical element having a linear polarization function, on a light
emission side of the light emitting element in this order from a light
emitting element side. Specifically, as illustrated in FIG. 1, a variable
circular polarizing unit 12 is arranged on top of a light emitting
surface side of an organic EL panel 11.

[0028]As described in detail later, the organic EL panel 11 is equivalent
to the display panel, and a positive electrode 32 of the organic EL panel
11 is equivalent to the reflection electrode. The variable circular
polarizing unit 12 is equivalent to the circular polarizing unit, a
(1/4)λ wavelength plate 41 constituting the variable circular
polarizing unit 12 is equivalent to the retardation plate, and a liquid
crystal element 42 is equivalent to the optical element (see FIGS. 1 and
4).

[0029]In the present invention, the light emitting element is configured
to synchronize with the light emission period within one frame to weaken
the linear polarization function of the optical element, and the light
emitting element is configured to synchronize with the non-light emission
period within one frame to intensify the linear polarization function of
the optical element. When the linear polarization function is weakened,
the light reflected from the reflection electrode is easily shielded. On
the other hand, when the linear polarization function is intensified, the
light reflected from the reflection electrode is not easily shielded and
is easily transmitted. A plurality of light emitting elements are
arranged on the display panel, and the display panel comprises a
controlling unit that sets the plurality of light emitting elements to a
light emitting state or a non-light emitting state all together. In that
case, the optical element in the circular polarizing unit can be one
liquid crystal element corresponding to the whole area of the plurality
of light emitting elements.

[0030]A plurality of light emitting elements may be arranged in a matrix
in the display panel, and the display panel may comprise a controlling
unit that sets one row or an arbitrary number of rows of the light
emitting elements to a light emitting state or a non-light emitting
state. In that case, the optical element in the circular polarizing unit
may be a plurality of liquid crystal elements corresponding to the whole
area of the light emitting elements in the arbitrary number of rows.

[0031]The light emitting element can be an organic electroluminescence
element.

[0032]<Organic EL Panel>

[0033]The organic EL panel 11 will be described first.

[0034]FIG. 2 is a schematic diagram illustrating an example of an organic
EL panel according to the embodiments of the present invention.

[0035]As illustrated in FIG. 2, the organic EL panel 11 includes a signal
line driving circuit 21 that applies a signal voltage corresponding to
image information to a signal line, a scanning line driving circuit 22
that drives a scanning line, a pixel circuit 23 that controls an electric
current applied to pixels in accordance with a signal voltage value, and
a light emission period control line driving circuit 24 that controls the
light emission period. The light emission period control line driving
circuit and a light emission period control line correspond to the
controlling unit that sets the light emitting state and the non-light
emitting state.

[0036]<Organic EL Element>

[0037]FIG. 3 is a schematic enlarged cross-sectional view illustrating an
example of an organic EL element that is a typical light emitting element
of an organic EL panel.

[0038]In the organic EL element, a positive electrode (reflection
electrode) 32, a hole transporting layer 33, a light emission layer 34,
an electron transporting layer 35, an electron injection layer 36, and a
negative electrode (half-light transmitting electrode) 37 are
sequentially arranged on a substrate 31. When an electric current is
applied to the organic EL element, holes injected from the positive
electrode 32 and electrons injected from the negative electrode 37
recombine in the light emission layer 34, and light is emitted. The
layers of the hole transporting layer 33, the light emission layer 34,
the electron transporting layer 35, and the electron injection layer 36
will be called organic compound layers.

[0039]Although an example of a configuration of forming the positive
electrode 32 on the substrate 31 is illustrated in the embodiments, the
negative electrode (reflection electrode) 37, the organic compound
layers, and the positive electrode (half-light transmitting electrode) 32
may be arranged on the substrate 31 in this order. The selection of
electrodes and the order of lamination of the layers are not particularly
limited. Although the embodiments illustrate a top-emission type display
apparatus in which the light emission is extracted from the half-light
transmitting electrode 37 on the opposite side of the substrate 31, the
present invention can also be applied to a bottom-emission type display
apparatus.

[0040]Organic compound materials used for the hole transporting layer 33,
the light emission layer 34, the electron transporting layer 35, and the
electron injection layer 36 may include low-molecular materials,
high-molecular materials, or both. The organic compound materials are not
particularly limited, and known materials can be used as necessary. The
organic EL element needs to be protected from the outside air such as
moisture. Therefore, for example, the organic EL element may be placed
between glasses or may be protected by an inorganic film, and the method
is not particularly limited.

[0041]Although the device configuration of the organic EL panel 11 has
been described, the organic EL panel 11 may be an organic EL panel
including organic EL elements of R, G, and B three colors or including
color filters arranged on top of a white organic EL element. Although the
organic EL element has been described as the light emitting element, any
element may be applied as long as the element is a light emitting element
including a reflection electrode.

[0044]As illustrated in FIG. 4, the variable circular polarizing unit 12
includes the (1/4)λ wavelength plate 41 and the liquid crystal
element 42. In the liquid crystal element 42, light transmitting
electrodes 45 and 46 and oriented films 47 and 48 are formed on glass
substrates 43 and 44, and a liquid crystal 49 is placed between the glass
substrates 43 and 44. The liquid crystal 49 is a guest host liquid
crystal in which a nematic liquid crystal 410 and a two-color pigment 411
are mixed, and the liquid crystal 49 indicates positive dielectric
anisotrophy. A uniaxial orientation process is applied to the oriented
films 47 and 48. In that case, liquid crystal molecules are horizontally
oriented when a voltage is not applied to the liquid crystal 49, i.e.
when the linear polarization function is weakened. The liquid crystal
molecules are vertically orientated when a voltage is applied to the
liquid crystal 49, i.e. when the linear polarization function is
intensified. The optical axis of the (1/4)λ wavelength plate 41 is
arranged to form a 45 degree angle with the orientation axis of the
liquid crystal element 42.

[0045]The nematic liquid crystal 410 is substantially horizontally
oriented along the glass substrates 43 and 44 in accordance with the
oriented film when a voltage is not applied to the liquid crystal element
42. In this case, the major axis direction of the two-color pigment 411
is also arranged in the same way in accordance with the nematic liquid
crystal 410. Therefore, in this state, one direction of the light
entering the liquid crystal element 42 is absorbed by the two-color
pigment 411. As a result, the liquid crystal element 42 functions as a
linear polarization plate.

[0046]In this way, the liquid crystal element 42 functioning as a linear
polarization plate and the (1/4)λ wavelength plate 41 are combined,
and the variable circular polarizing unit 12 functions as a circular
polarizing plate. Therefore, in this case, the external light reflection
is reduced, and the transmittance of the emitted light is approximately
halved.

[0047]On the other hand, the nematic liquid crystal 410 is vertically
oriented relative to the glass substrates 43 and 44 when a voltage is
applied to the liquid crystal element 42. In this case, the major axis
direction of the two-color pigment 411 is also arranged in the same way
in accordance with the nematic liquid crystal 410. Therefore, in this
state, the light entering the liquid crystal element 42 is transmitted
without being absorbed by the two-color pigment 411.

[0048]Therefore, the liquid crystal element 42 does not function as a
linear polarization plate, and the transmittance of the emitted light is
still high even if the liquid crystal element 42 is combined with the
(1/4)λ wavelength plate 41. More specifically, the external light
reflection of the variable circular polarizing unit 12 is larger when a
voltage is applied, compared to when a voltage is not applied. However,
the transmittance of the emitted light is high, and the transmittance of
the emitted light is higher than that in a normal circular polarizing
plate.

[0049]The foregoing is an example of a liquid crystal element using a
nematic liquid crystal. In an application requiring high speed response
during ON/OFF of the electric field, the nematic liquid crystal may not
be used because the response speed is slow. Republished Patent
Application No. WO2005/090520 discloses a high-molecular stabilized blue
phase liquid crystal and describes that the response time is about 100
μsec.

[0050]<High Speed Response Element>

[0051]FIGS. 9A and 9B illustrate a structure of a high speed response
element as an example of a variable circular polarizing unit used in the
image display apparatus according to the embodiments of the present
invention.

[0052]As illustrated in FIGS. 9A and 9B, in the high speed response
element, a comb-shaped electrode 1 is arranged on a substrate (not
shown), such as a glass, within the same plane, and an electric field 2
is applied in parallel to a substrate surface. The other substrate is
sandwiched by glass plates without electrode through a spacer, and a
high-molecular stabilized blue liquid crystal material (liquid crystal 3)
is injected to the generated gap.

[0053]As illustrated in FIG. 9A, the liquid crystal 3 is oriented in the
direction of the electric field when a voltage is applied to the
comb-shaped electrode 1. Uniaxial refractive index anisotrophy is
generated, and the high speed response element functions as a linear
polarization plate. A function as a circular polarizing plate is
generated by combining the high speed response element with the
(1/4)λ wavelength plate 4 having a 45 degree optical axis 5.

[0054]Meanwhile, as illustrated in FIG. 9B, the liquid crystal 3 is
randomly oriented when the electric field is turned off. The function of
the circular polarizing plate disappears, and light can be transmitted.

[0056]A synchronization operation of the organic EL panel 11 and the
variable circular polarizing unit 12 will be described with reference to
FIGS. 5A to 5C. FIGS. 5A to 5C are timing charts describing an operation
of an organic EL panel and a variable circular polarizing unit.

[0057]FIG. 5A illustrates a drive sequence of the organic EL panel 11. As
illustrated in FIG. 5A, the scanning line driving circuit 22 that drives
a scanning line sequentially writes signal voltages corresponding to
image information to the pixel circuit 23 in a period A. It is desirable
to light up the whole area all together in a period B after the signal
voltages are written to all pixels. A combination of one period A
(writing period of signal voltage) and one period B (period that the
light emitting element emits light) will be called one frame.

[0059]As illustrated in FIGS. 5B and 5C, a voltage is not applied to the
liquid crystal element 42 in the period A, and the variable circular
polarizing unit 12 functions as a circular polarizing plate. The
operation reduces the external light reflection in the period A. In this
case, since the organic EL panel 11 does not emit light, the light
emission is not lost.

[0060]A voltage is applied to the liquid crystal element 42 in the period
B to increase the transmittance of the emitted light in the variable
circular polarizing unit 12. As a result of the operation, the light
emission of the organic EL panel 11 can be efficiently extracted in the
period B, compared to a normal circular polarizing plate. Since the
variable circular polarizing unit 12 does not function as a circular
polarizing plate in the period B, the external light reflection
increases.

[0061]More specifically, the direction of orientation of the liquid
crystal element is controlled so that the ratio of light emitted from the
light emitting element transmitting through the retardation plate and the
liquid crystal element is larger in the light emission period within one
frame in the drive of the light emitting element than in the non-light
emission period.

[0062]Therefore, the amount of external light reflection varies depending
on the ratio of the period A and the period B. The amount of external
light refection can be reduced when the period of lighting up in the
whole area is shorter, and the visibility improves.

[0063]The image display apparatus of the present invention will be
described in further detail based on specific embodiments.

First Embodiment

[0064]A schematic configuration of the image display apparatus of a first
embodiment is the same as the configuration illustrated in FIG. 1. A
summary of the organic EL panel of the first embodiment is the same as
the summary illustrated in FIG. 2.

[0065]FIG. 6 illustrates an example of configuration of a pixel circuit
including an organic EL element of the first embodiment.

[0066]In FIG. 6, P1 denotes a scanning line, and P2 denotes a light
emission period control line. A signal voltage is input from the signal
line in accordance with image information. A positive electrode of the
organic EL element is connected to a drain terminal of a TFT (M3), and a
negative electrode is connected to a ground potential CGND. Hereinafter,
a brief operation of the pixel circuit will be described.

[0067]When the signal voltage is written, a signal of HI level is input to
the scan signal P1, and a signal of LOW level is input to P2. A
transistor M1 is ON, and M3 is OFF. At this point, M3 is not conductive,
and an electric current does not flow through the organic EL element.
Based on the signal voltage, a voltage corresponding to the electric
current drive capability of M1 is generated in a capacity C1 arranged
between a gate terminal of M2 and a power potential V1.

[0068]A signal of LOW level is input to P1, and a signal of LOW level is
input to P2 to shut off the electric current flowing through the organic
EL element while maintaining the written signal voltage. At this point,
the transistors M1 and M3 are OFF. Since M3 is not conductive, the supply
of electric current to the organic EL element can be shut off, and a
non-light emitting state can be set.

[0069]A signal of LOW level is input to P1, and a signal of HI level is
input to P2 to supply an electric current to the organic EL element in
accordance with the maintenance of the written signal voltage. At this
point, the transistor M1 is OFF, and M3 is ON. Since M3 is conductive, an
electric current corresponding to the electric current drive capability
of M2 is supplied to the organic EL element based on the voltage
generated in C1, and the organic EL element emits light with luminance
corresponding to the supplied electric current.

[0070]In this way, switching HI/LOW of the signal level input to P2 can
arbitrarily control the light emission period.

[0071]Although the configuration of FIG. 2 is implemented for the pixel
circuit in the first embodiment, the pixel circuit is not limited to
this. Any configuration can be implemented as long as the drive
system/pixel circuit can control the light emission period.

[0072]An operation of the entire organic EL panel will be described.

[0073]In the organic EL panel of the first embodiment, signal voltages
corresponding to image information that the pixels should display are
simultaneously written to the pixels of the pixel group connected to one
scanning line during one horizontal period. Similarly, signal voltages
are sequentially written to pixel groups connected to scanning lines of
the following rows. Writing to all pixels is finished within a period
shorter than one vertical period. For example, one vertical period is
16.67 [msec] in the case of an organic EL panel at 60 Hz drive. The
organic EL panel of the first embodiment has a matrix arrangement of N
rows and M columns. The scanning line P1 connected to the pixel circuit
of an n-th row of the organic EL panel is designated with P1n, and a
light emission period control line is designated with P2n (N, n, and M
are natural numbers, 1≦n≦N).

[0074]FIG. 7 illustrates a timing chart of scanning lines of a first row,
an n-th row, and an N-th row according to the first embodiment.

[0075]<Period A/Writing Period of Signal Voltage>

[0076]Writing to the n-th row of the organic EL panel is performed when
P1n is HI and P2n is LOW, and the image information is stored in the
pixel circuit in accordance with the signal voltage input from the signal
line. Subsequently, P1n becomes LOW and P2n becomes LOW, and an electric
current can be applied to the organic EL element in accordance with the
stored information. However, a transistor M3 is turned off because P2n is
LOW, and the electric current does not flow through the organic EL
element. In this state, writing to the next row (n+1) is performed, and
writing from the first row to the N-th row is finished without applying
the electric current to the organic EL element. The period A is 15.00
[msec] here, and writing of the signal voltages corresponding to the
image information to all pixel circuits is finished within the period.
The organic EL element does not emit light in the period.

[0077]<Period B/Period that All Pixels Emit Light>

[0078]When writing of the signal voltages to all pixels is finished in the
period A, all pixels emit light all together. For example, in the pixels
of the n row of the organic EL panel, P1n is set to LOW, and P2n is set
to HI (transistor M3 is ON). An electric current flows through the
organic EL element in accordance with the signal voltages stored in the
pixel circuits, and the organic EL element emits light. The period B is
1.67 msec here, and the organic EL element emits light only in the
period.

[0079]<Variable Circular Polarizing Unit>

[0080]The variable circular polarizing unit 12 will be described.

[0081]The light transmitting electrodes 45 and 46 arranged on the glass
substrates 43 and 44 of the liquid crystal element 42 are formed all
together throughout the whole area of the region corresponding to the
organic EL panel. Therefore, the linear polarization function can be
adjusted all together throughout the whole area in the liquid crystal
element 42.

[0082]In the period A, a voltage is not applied to the liquid crystal
element 42 of the variable circular polarizing unit 12, and the variable
circular polarizing unit 12 functions as a circular polarizing plate. The
operation reduces the external light reflection in the period A. The
period A is a non-light emission period in which the organic EL panel 11
does not emit light, and the light emission is not lost.

[0083]A voltage is applied to the liquid crystal element 42 of the
variable circular polarizing unit 12 in the period B to increase the
transmittance of the variable circular polarizing unit 12. As a result of
the operation, the light emission of the organic EL panel 11 can be more
efficiently extracted in the period B, compared to a normal circular
polarizing plate. The period B is a light emission period.

[0084]Therefore, the first embodiment can provide an organic EL panel with
excellent extraction efficiency of emitted light, compared to when a
typical circular polarizing plate is used. Simply put, a display with
about twice the luminance as that of a conventional display can be
provided. The power consumption can be approximately halved when compared
under the same luminance.

[0085]As for the external light reflection, a similar effect as the
circular polarizing plate can be obtained in the period A. Although the
amount of the external light reflection increases in the period B, the
time of the period B is about 1/10 of that of the period A. Therefore, as
for the external light reflection, excellent visibility close to when the
circular polarizing plate is used can be obtained.

[0086]The effect of the circular polarizing plate increases if the period
B is less than 1/5 of the period A. The period B can be less than 1/10 of
the period A, and it is optimal that the period B is less than 1/20 of
the period A. Meanwhile, the period B is short if the period B is less
than 1/30 of the period A, and the lifetime of the organic EL panel
becomes short. Therefore, it is desirable that the period B is equal to
or greater than 1/30 of the period A.

[0087]The light transmitting electrodes 45 and 46 formed on the liquid
crystal element 42 may be formed all together throughout the whole area
of the region corresponding to liquid crystal element 42, and the drive
system of the liquid crystal element 42 may be simple. Therefore, the
variable circular polarizing unit can be inexpensively provided.

Second Embodiment

[0088]In the first embodiment, the light emission period and the non-light
emission period of the organic EL panel 11 are controlled all together
throughout all pixels, and the drive of the variable circular polarizing
unit 12 is controlled all together throughout the whole area. In a second
embodiment, the periods and the drive are controlled row by row.

[0089]The configuration of a pixel circuit of the second embodiment
including an image display apparatus, an organic EL panel, and an organic
EL element is the same as the configuration of the first embodiment.

[0090]An operation of the entire organic EL panel will be described.

[0091]As in the first embodiment, the organic EL panel of the second
embodiment has a matrix arrangement of N rows and M columns. The scanning
line P1 connected to the pixel circuit of an n-th row of the organic EL
panel is designated with P1n, and the light emission period control line
is designated with P2n (N, n, M, and m are natural numbers,
1≦n≦N).

[0092]FIG. 8 illustrates a timing chart of signal lines of a first row, an
n-th row, and an N-th row according to the second embodiment.

[0093]<Period An/Writing Period of Signal Voltage>

[0094]Writing to the n row of the organic EL panel is performed when P1n
is HI and P2n is LOW, and information is stored in the pixel circuit in
accordance with signal voltages input from the signal lines. The time of
a period An is (16.67/N(msec)) here, and writing of a signal voltage to
the pixel circuit of the n-th row is finished within the period. The
organic EL element does not emit light in the period. After the
operation, a writing operation to the next row starts.

[0095]<Period Bn/Period that Organic EL Element Emits Light>

[0096]After the period An, P1n is LOW and P2n is HI in the control signal
for the n-th row of the organic EL panel. The transistor M3 turns on, and
an electric current flows through the organic EL element in accordance
with the image information stored in the pixel circuit. As a result, the
organic EL element emits light with brightness corresponding to the image
information.

[0097]<Period Cn/Period that Organic EL Element Does Not Emit Light>

[0098]After the period Bn, P1n is LOW and P2n is LOW in the control signal
for the n-th row of the organic EL panel. Although the image information
is already stored in the pixel circuit, the transistor M3 is OFF, and an
electric current does not flow through the organic EL current. Therefore,
the organic EL element does not emit light.

[0099]In other words, the periods An and Cn are non-light emission periods
in which the organic EL element does not emit light, and the period Bn is
a light emission period in which the organic EL element emits light.

[0100]<Variable Circular Polarizing Unit>

[0101]The variable circular polarizing unit 12 will be described.

[0102]One of the light transmitting electrodes 45 and 46 included in the
glass substrates 43 and 44 of the liquid crystal element 42 is formed all
together throughout the whole area of the region corresponding to the
organic EL panel, and the other is patterned with stripes according to
the row direction of the organic EL panel 11. As a result, the liquid
crystal element 42 can adjust the linear polarization function row by
row.

[0103]In the periods An and Cn, a voltage is not applied to the liquid
crystal element 42 of the variable circular polarizing unit 12, and the
variable circular polarizing unit 12 functions as a circular polarizing
plate. The operation reduces the external light refection in the periods
An and Cn. At this point, the organic EL panel 11 does not emit light,
and the light emission is not lost.

[0104]In the period Bn, a voltage is applied to the liquid crystal element
42 of the variable circular polarizing unit 12 to increase the
transmittance of the variable circular polarizing unit 12. As a result of
the operation, the light emission of the organic EL panel 11 can be
efficiently extracted in the period Bn, compared to a normal circular
polarizing plate.

[0105]Therefore, as in the first embodiment, an organic EL panel with
excellent extraction efficiency of emitted light can be provided,
compared to when a typical circular polarizing plate is used. As for the
external light reflection, excellent visibility close to when the
circular polarizing plate is used can be obtained.

[0106]The light transmitting electrode formed on the liquid crystal
element 42 may be patterned with lines corresponding to the row layout of
the panel, and the drive system of the liquid crystal element 42 may also
be simple. Therefore, the variable circular polarizing unit can be
inexpensively provided.

Third Embodiment

[0107]In the second embodiment, the light emission period and the
non-light emission period of the organic EL panel 11 are controlled row
by row, and the drive of the variable circular polarizing unit 12 is also
controlled in accordance with the row-by-row control of the organic EL
panel 11. In a third embodiment, the periods and the drive are controlled
by an arbitrary number of rows. An example of a configuration of
controlling two rows by two rows will be illustrated below.

[0108]A configuration of a pixel circuit including an image display
apparatus, an organic EL panel, and an organic EL element of the third
embodiment is the same as that of the first embodiment.

[0109]An operation of the entire organic EL panel will be described.

[0110]As in the first embodiment, the organic EL panel of the third
embodiment has a matrix arrangement of N rows and M columns, the scanning
line P1 connected to the pixel circuit of an n-th row of the organic EL
panel is designated with P1n, and the light emission period control line
is designated with P2n (N, n, M, and m are natural numbers,
1≦n≦N).

[0111]FIG. 10 illustrates a timing chart of signal lines of a first row, a
second row, a (2n-1)-th row, and a (2n)-th row according to the third
embodiment. The control of light emission of the organic EL panel two
rows by two rows will be described, and an operation of a k-th row (k is
a natural number) will be described.

[0112]<Period Ak/Writing Period of Signal Voltage>

[0113]Writing to the k-th row of the organic EL panel is performed when
P1k is HI and P2k is LOW, and information is stored in the pixel circuit
in accordance with the signal voltages input from the signal lines. The
time of the period Ak is (16.67/N[msec]) here, and writing of the signal
voltages to the pixel circuit of the k-th row is finished within the
period. The organic EL element does not emit light in the period. After
the operation, a writing operation of the next row starts.

[0114]<Period Bk/Period that Organic EL Element Emits Light>

[0115]In the control signal for the k-th row of the organic EL panel, P1k
is LOW, and P2k is HI. The transistor M3 turns on, and an electric
current flows through the organic EL element in accordance with the image
information stored in the pixel circuit. As a result, the organic EL
element emits light with brightness corresponding to the image
information.

[0116]<Period Ck/Period that Organic EL Element Does Not Emit Light>

[0117]In the control signal for the k-th row of the organic EL panel, P1k
is LOW, and P2k is LOW. Although the image information is already stored
in the pixel circuit, the transistor M3 is turned off, and the electric
current does not flow through the organic EL element. Therefore, the
organic EL element does not emit light.

[0118]In other words, the periods An and Cn are non-light emission periods
in which the organic EL element does not emit light, and the period Bn is
a light emission period in which the organic EL element emits light.

[0119]As illustrated in FIG. 10, light emission period control signals
P2(2n-1) and P2(2n) input to adjacent (2n-1)-th row and (2n)-th row are
the same in order to make the timing of the light emission periods
(period B) of the organic EL element of the (2n-1)-th row and the (2n)-th
row the same. As a result, the light emission is controlled two rows by
two rows.

[0120]Although the two-row-by-two-row control of the light emission period
and the non-light emission period of the organic EL panel has been
described, the number of rows is not limited to this. More specifically,
the number of lit rows can be arbitrarily set if the same light emission
period control signal P2 is input to the arbitrary number of rows.

[0121]<Variable Circular Polarizing Unit>

[0122]The variable circular polarizing unit 12 will be described.

[0123]One of the light transmitting electrodes 45 and 46 included in the
glass substrates 43 and 44 of the liquid crystal element 42 is formed all
together throughout the whole area corresponding to the organic EL panel,
and the other is patterned with stripes in accordance with the arbitrary
number of rows for emitting light at the same timing of the organic EL
panel 11. Therefore, the liquid crystal element 42 can adjust the linear
polarization function in accordance with each light emission region and
each timing of the organic EL panel 11.

[0124]The operation of the variable circular polarizing unit 12 is the
same as that of the second embodiment.

[0125]Therefore, as in the first embodiment, an organic EL panel with
excellent extraction efficiency of emitted light can be provided,
compared to when a typical circular polarizing plate is used. As for the
external light reflection, excellent visibility close to when the
circular polarizing plate is used can be obtained.

[0126]The light transmitting electrode formed on the liquid crystal
element 42 may be patterned with lines corresponding to the row layout of
the organic EL panel, and the drive system of the liquid crystal element
42 may also be simple. Therefore, the variable circular polarizing unit
can be inexpensively provided.

Fourth Embodiment

[0127]In a fourth embodiment, the above-mentioned high-molecular
stabilized blue phase liquid crystal is used for the liquid crystal
element of the variable circular polarizing unit 12. Other content,
operations, and effects are the same as those of the first and second
embodiments.

[0128]The material disclosed in the above-mentioned document (Republished
Patent Application No. WO2005/090520) is used and injected to a cell
forming the comb-shaped electrode, and a phase forming plate is further
attached to create the high speed response element using the
high-molecular stabilized phase liquid crystal.

[0129]Although the optical element that controls the linear polarization
of the variable circular polarizing unit 12 is a liquid crystal element
in the description, the element is not limited to this.

[0130]While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0131]This application claims the benefit of Japanese Patent Application
No. 2009-224327, filed on Sep. 29, 2009, which is hereby incorporated by
reference herein in its entirety.